Integrated process to recover high quality native CO2 from a sour gas comprising H2S and CO2

ABSTRACT

The invention concerns a method for treating a hydrocarbon feed gas stream containing at least CO 2  and H 2 S to recover a high quality purified CO 2  gas stream, comprising a. Separating said hydrocarbon feed gas stream into a sweetened hydrocarbon gas stream, and an acid gas stream; b. Introducing said gas stream into a Claus unit, c. Introducing the tail gas into a hydrogenation reactor and then into a quench contactor of the Tail Gas Treatment Unit (TGTU); d. Contacting said tail gas stream with a non-selective amine-based solvent into a non-selective acid gas absorption unit of the TGTU; e. Sending the off gas to an incinerator; f. Contacting said enriched gas stream (vii) with a selective H 2 S-absorption solvent into a selective H 2 S-absorption unit thereby recovering a highly purified CO 2  gas stream and a H 2 S-enriched gas stream, as well as the device for carrying said method.

RELATED APPLICATIONS

The present application is a Continuation of U.S. patent application Ser. No. 14/651,074 filed Jun. 10, 2015 which is a National Phase entry of PCT Application No. PCT/M2013/002901, filed Dec. 10, 2013, which claims priority to U.S. Provisional Application No. 61/735,301, Filed Dec. 10, 2012, and also claims priority to U.S. Provisional Application No. 61/752,174, filed Jan. 14, 2013, said applications being hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to the removal of sulfur components and carbon dioxide contained in a hydrocarbon feed stream in order to recover the native carbon dioxide in a purified stream. More specifically, the present invention relates to a process for recovering high quality native CO₂ from a sour gas which comprises CO₂, H₂S and other sulfur contaminants, so that said recovered high quality native CO₂ may be then sequestered or used for enhanced oil recovery (EOR). Besides, the present invention concerns an installation for implementing such process.

BACKGROUND OF THE INVENTION

Natural gas or gases associated to oil productions produced from geological reservoirs, or refinery acid gases often contain(s) acid contaminants, such as carbon dioxide and/or hydrogen sulfide and/or other sulfur contaminants, such as carbonyl sulfide, carbon disulfide and mercaptans. For most of the applications of these gas streams, the acid contaminants need to be removed, either partially or almost completely, depending on the application and the type of contaminant.

Methods to remove carbon dioxide and/or hydrogen sulfide and/or other sulfur contaminants from a hydrocarbon gas stream are known in the prior art.

One common approach to remove acid contaminants involves the use of solvents such as chemical solvent (amine-based solvent), hybrid solvent or physical solvent. These solvents have been largely disclosed in the art. However, if appreciable levels of sulfur compounds are present in the acid gas, the most common process to eliminate hydrogen sulfide is to convert said hydrogen sulfide into a non-hazardous by-product such as elemental sulfur. The Claus process is a known type of sulfur recovery process allowing the conversion of hydrogen sulfide into elemental sulfur, by sending it to a sulfur recovery unit (SRU).

In some embodiments, remaining H₂S traces are captured in a Tail Gas Treatment Unit (TGTU), positioned at the outlet of the Claus unit to increase significantly sulfur recovery, and then be recycled into the Claus unit. The TGTU converts small amounts of sulfur compounds (<5%), which were not converted in the sulfur recovery unit (SRU), into hydrogen sulfide (H₂S) and recycles it back to the SRU for additional processing. The TGTU is composed of at least four equipments: a hydrogenation reactor, a waste heat exchanger, a quench tower and an acid gas absorption column.

The SRU tail gas is heated and sent to the hydrogenation reactor where essentially all of the sulfur compounds are converted into H₂S. The gas from the hydrogenation reactor is cooled in the waste heat exchanger and the quench tower. The cooled gas is then sent to the acid gas absorption column, where amine removes the H₂S and some of the CO₂ contained in the gas stream. The H₂S and CO₂ removed from the amine is cooled (and water removed) in the overhead condenser and recycled to the sulfur recovery unit for additional processing into sulfur. At the outlet of the TGTU, native CO₂ is recovered. It is diluted by a large amount of nitrogen coming from the combustive agent used for Claus combustion. To recover a purified CO₂ stream, CO₂ capture technologies using solvent (for example an amine solvent, such as MethylEthanolAmine (MEA)) can be used. However, since the CO₂ is diluted in a large volume of nitrogen, the amine-based CO₂ capture unit requires large size equipments, thereby leading to huge CAPEX and OPEX.

Furthermore, an incinerator is generally connected at the outlet of the amine-based CO₂ capture unit in order to incinerate the nitrogen, the hydrogen, the carbon monoxide and the remaining traces of sulfur contaminants.

At the outlet of the amine-based CO₂ capture unit a purified stream of native CO₂ is recovered, however this CO₂ stream contains hydrogen sulfide in such quantities that do not meet certain specifications, and more particularly such purified CO₂ cannot be used for enhanced oil recovery (EOR) applications.

Therefore, there is a need for a method that allows recovering high quality native CO₂ from a hydrocarbon feed gas stream which contains acidic compounds, such as CO₂, H₂S and other sulfur contaminants, with better purity compared with the processes of the prior art.

SUMMARY OF THE INVENTION

Method

An object of the present invention is a method for treating a hydrocarbon feed gas stream containing at least carbon dioxide and hydrogen sulfide to recover a high quality purified CO₂ gas stream, said process comprising the following steps:

-   -   a. Separating said hydrocarbon feed gas stream into (i) a         sweetened hydrocarbon gas stream, and (ii) an acid gas stream         comprising at least carbon dioxide and hydrogen sulfide;     -   b. Introducing said acid gas stream (ii) into a Claus unit,         thereby recovering (iii) a liquid stream of elemental sulfur         and (iv) a tail gas comprising nitrogen, carbon dioxide, sulfur         dioxide and hydrogen sulfide;     -   c. Introducing the exiting tail gas (iv) into a hydrogenation         reactor and then to a quench contactor of a Tail Gas Treatment         Unit (TGTU) thereby recovering (v) a hydrogenated tail gas         stream comprising nitrogen, hydrogen, carbon monoxide, carbon         dioxide and hydrogen sulfide;     -   d. Contacting said hydrogenated tail gas (v) with a         non-selective amine-based solvent into a non-selective acid gas         absorption unit of the TGTU thereby recovering (vi) an off gas         comprising nitrogen, hydrogen and carbon monoxide and (vii) a         gas stream enriched in carbon dioxide and hydrogen sulfide;     -   e. Sending the off gas (vi) to an incinerator;     -   f. Contacting said enriched gas stream (vii) with a selective         H₂S-absorption solvent into a selective H₂S-absorption unit         thereby recovering (viii) a highly purified CO₂ gas stream         and (ix) a H₂S-enriched gas stream.

In one embodiment, the feed gas stream is separated in step a) into (i) a sweetened hydrocarbon gas stream, and (ii) an acid gas stream comprising carbon dioxide and hydrogen sulfide. Said separation can be performed by a classical sweetening method using a chemical, a hybrid or a physical solvent.

In one embodiment, the hybrid solvent comprises amine, water and thiodiglycol (TDG). Preferably, the amine is selected from the group comprising DiEthanolAmine (DEA), MethylDiEthanolAmine (MDEA), HydroxyEthylPiperazine (HEP), Piperazine (PZ) and mixtures thereof.

In one embodiment, the non-selective amine-based solvent used in the non-selective acid gas absorption unit of the TGTU is MonoEthanolAmine (MEA).

In one embodiment, the TGTU further comprises a feed inline burner or a tail gas heater. The acid gas absorption unit may be based on amine.

In one embodiment, the selective H₂S-absorption solvent used in the selective H₂S-absorption unit is MethylDiEthanolAmine (MDEA). Preferably, said selective H₂S-absorption solvent is a hybrid solvent comprising an amine, water and thiodiglycol (TDG). Preferably, said amine is selected between DiEthanolAmine (DEA), MethylDiethanolAmine (MDEA), HydroxyEthylPiperazine (HEP) and Piperazine (PZ).

In one embodiment, the H2S-enriched gas stream (ix) recovered at the exit of the selective H₂S-absorption unit is recycled upstream of or directly to the Claus unit.

In one embodiment, the H₂S-enriched stream may contain at least 25% of hydrogen sulfide, preferably at least 40% of hydrogen sulfide, and more preferably at least 50% of hydrogen sulfide.

In one embodiment, the highly purified CO₂ stream obtained by the method of the invention may contain less than 250 ppm of H₂S, in particular less than 100 ppm of H₂S.

Device

The present invention also relates to a device for carrying out the method as described above, as well as the purified gas stream obtained by the present process.

The device of the present invention comprises in the direction of flow:

-   -   an acid gas removal unit;     -   a Claus unit;     -   a tail gas treatment unit comprising a hydrogenation reactor, a         quench contactor and a non-selective acid gas absorption unit;     -   a selective H₂S-absorption unit; and     -   an incinerator.

In one embodiment, the acid gas removal unit is an amine based solvent.

In one embodiment, the tail gas treatment unit further comprises a feed inline burner or a tail gas heater. The non-selective acid gas absorption unit is based on an amine.

In one embodiment, the non-selective amine-based solvent used in the non-selective acid gas absorption unit of the TGTU is MonoEthanolAmine (MEA).

In one embodiment, the device comprises a line for recycling the H2S-enriched gas stream recovered at the exit of the selective H2S-absorption unit upstream of or directly to the Claus furnace.

In one embodiment the H₂S-enriched gas stream may contain at least 10% of hydrogen sulfide, preferably at least 20% of hydrogen sulfide, and more preferably at least 80% of hydrogen sulfide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a classical CO2 recovery unit, as known in the prior art.

FIG. 2 is a schematic view of the high-quality native CO2 recovery unit for performing the method of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The process according to the invention applies to the treatment of a hydrocarbon feed gas stream containing acid contaminants, such as a natural gas stream. The acid contaminants are mainly composed of carbon dioxide and hydrogen sulfide. However, the gas stream may also contain other acid contaminants, such as mercaptans, and/or carbonyl sulfide, and/or carbon disulfide, etc.

Typically, the hydrocarbon feed gas stream may contain from 5% to 70% of CO₂, in particular from 7% to 40% of CO₂, more particularly from 10% to 20% of CO₂, and from 1% to 40% of H₂S, in particular from 2% to 20% of H₂S, more particularly from 3% to 10% of H₂S.

According to step a) of the method of the invention, the hydrocarbon gas stream is separated into (i) a sweetened hydrocarbon gas stream, and (ii) an acid gas stream comprising at least carbon dioxide and hydrogen sulfide.

By “sweetened hydrocarbon gas stream”, it is meant a hydrocarbon gas stream containing less acid contaminants than the hydrocarbon feed gas stream. The acid gas stream (ii), on the other hand, is enriched in acid contaminants compared to the hydrocarbon feed gas stream.

Methods for obtaining a sweetened hydrocarbon gas stream (i) and acid gas stream (ii) from a hydrocarbon feed gas stream containing acid contaminants are well known by the person skilled in the art. Any sweetening method may be used for performing step a) of the present invention. Such methods include cryogenic treatment or solvent treatment, such as chemical, physical or hybrid solvent.

Typically, the acid gas stream (ii) contains from 15% to 75% of CO₂, in particular from 30% to 65% of CO₂, more particularly from 40% to 60% of CO₂, and from 20% to 80% of H₂S, in particular from 40% to 70% of H₂S, more particularly from 50% to 70% of H₂S.

According to step b) of the method of the invention, the acid gas stream (ii) is then introduced into a Claus unit thereby recovering (iii) a liquid stream of elemental sulfur and (iv) a tail gas mainly comprising nitrogen, carbon dioxide, sulfur dioxide and hydrogen sulfide.

A Claus unit allows the conversion of hydrogen sulfide into elemental sulfur according to the following reactions: 2 H₂S+3 O₂→2 SO₂+2 H₂O  (1) 2 H₂S+SO₂⇄3 S+2 H₂O  (2)

According to the invention, the tail gas (iv) recovered at the exit of the Claus unit mostly contains nitrogen, carbon dioxide, sulfur dioxide, hydrogen sulfide and water. Said tail gas (iv) generally contains at least 40% of N2, preferably from 40% to 70% of N2, and at least 10% of CO2, in particular from 10% to 75% of CO2 as main components, and less than 4% of SO2, in particular less than 2% of SO2, and less than 4% of H2S, in particular less than 2% of H2S.

In one embodiment of step c) of the method of the invention, the tail gas (iv) exiting the Claus unit is introduced into a feed inline burner or a tail gas heater before being introduced into the hydrogenation reactor of the Tail Gas Treatment Unit (TGTU) thereby recovering (v) a hydrogenated tail gas stream mainly comprising nitrogen, hydrogen, carbon monoxide, carbon dioxide and hydrogen sulfide.

According to the invention, the hydrogenated tail gas (v) recovered at the exit of the hydrogenation unit mostly contains nitrogen, hydrogen, carbon monoxide, carbon dioxide and hydrogen sulfide. Said tail gas (iv) generally contains at least 20% of N₂, preferably from 60% to 90% of N₂, and at least 5% of CO₂, in particular from 10% to 20% of CO₂ as main components, and less than 1.0% of CO, in particular less than 0.5% of CO, and less than 5% of H₂S, in particular less than 3% of H₂S.

In one embodiment, the TGTU comprises four main equipments in the direction of flow:

a feed inline burner or a tail gas heater for heating the tail gas stream,

a hydrogenation reactor for converting the sulfur compounds of the tail gas stream into H₂S,

a quench contactor for removing water from the gas stream and,

a non-selective acid gas absorption unit for separating the acid gases (mainly CO₂ and H₂S) from the other constituents of the hydrogenated tail gas stream.

The hydrogenation reactor typically comprises a catalytic bed where sulfur compounds such as SO₂, S, COS and CS₂ are converted into H₂S. Furthermore, the feed inline burner or tail gas heater positioned before the input of the hydrogenation reactor heats the tail gas to a temperature suitable for performing the hydrogenation, generally from 130° C. to 240° C., preferably around 225° C. The burner generally operates with air and fuel.

The converted gas stream recovered at the exit of the hydrogenation reactor is then passed through a quench contactor, preferably a water-quench tower, in order to remove all or part of water from the gas stream. The proportion of water removed from the gas stream is at least 60%, preferably at least 70%.

The water saturated gas stream exiting the quench tower is then passed through a non-selective acid gas absorption unit, wherein acidic compounds, mainly CO₂ and H₂S, are absorbed by a non-selective acid gas absorbing solution. The non-selective acid gas absorption unit is an amine-based unit. A gas stream enriched in carbon dioxide and hydrogen sulfide (vii) is thus recovered from the non-selective acid gas absorption unit, that contains less than 500 ppm of H₂S, preferably less than 100 ppm of H₂S.

The lean solution containing carbon dioxide and hydrogen sulfide and some other sulfur contaminants, such as carbonyl sulfide, carbon disulfide and mercaptans, is recovered and passed through a stripping column in order to separate the absorbing solution from the acidic contaminants. The absorbing solution is recovered at the bottom of the stripping column and may be recycled to the acid gas absorption unit. A gas stream enriched with sulfur compounds is recovered at the head of the column and may be recycled upstream of or directly in the Claus furnace.

According to step d) of the method of the invention, the hydrogenated tail gas (v) exiting the quench contactor is introduced into a non-selective acid gas absorption unit thereby separating said hydrogenated tail gas into (vi) an off gas mainly comprising nitrogen, hydrogen, and carbon monoxide, and (vii) a gas stream enriched in carbon dioxide and hydrogen sulphide. According to the invention, the off gas (vi) recovered at the exit of the non-selective acid gas absorption unit generally contains at least 70% of N₂, preferably from 70% to 80% of N₂, and at least 2% of H₂, in particular from 2% to 5% of H₂, and at least 0.1% of CO, in particular from 0.1% to 1% of CO.

According to the invention, the gas stream (vii) recovered at the exit of the acid gas absorption unit generally contains at least 90% of CO₂, preferably from 85% to 97% of CO₂, and at least 3% of H₂S, in particular from 0% to 10% of H₂S.

According to step e) of the method of the invention, the off gas (vi) is sent to an incinerator.

According to step f) of the method of the invention, the enriched gas stream (vii) is introduced into a selective H₂S-absorption unit, wherein H₂S is selectively absorbed by a selective H₂S-absorption solvent. Preferably, the selective H₂S-absorption solvent is an amine-based solvent but any other suitable solvent may be used. More preferably, the amine-based solvent is a MDEA-based solvent.

According to the invention, the highly purified CO₂ gas stream (viii) exiting the selective H₂S-absorption unit generally contains at least 90% of CO₂ (wet basis), preferably from 90% to 97% of CO₂, and less than 250 ppm of H₂S, in particular less than 100 ppm of H₂S.

In one embodiment, the H₂S-enriched gas stream (ix) exiting the selective H₂S-absorption unit is recycled upstream of or directly to the Claus furnace.

According to the invention, the H₂S-enriched gas stream (ix) exiting the selective H₂S-absorption unit generally contains at least 15% of H₂S, preferably from 15% to 30% of H₂S, and less than 80% of CO₂, in particular less than 70% of CO₂.

Another object of the present invention is a device for carrying the method of the invention as previously described, said device comprising in the direction of flow:

-   -   an acid gas removal unit;     -   a Claus unit;     -   a tail gas treatment unit comprising a hydrogenation reactor, a         quench contactor and a non-selective acid gas absorption unit;     -   a selective H₂S-absorption unit; and     -   an incinerator.

In one embodiment, the tail gas treatment unit (TGTU) further comprises a feed inline burner or a tail gas heater before the hydrogenation reactor.

The hydrogenation reactor preferably comprises a CoMo catalyst.

The quench contactor may comprise distillation trays or a column packing (random or structured) for direct contact of water.

The non-selective acid gas absorption unit preferably comprises a non-selective amine-based solvent. More preferably the non-selective amine-based solvent used in said non-selective absorption unit is an alcanolamine, in particular MonoEthanolAmine (MEA).

In one embodiment, the device comprises a selective H₂S-absorption unit based on a selective H₂S-absorption solvent. Preferably, said selective H₂S-absorption solvent is an alcanolamine. More preferably, said solvent is MDEA (MethylDiEthanolAmine).

In one embodiment, the device comprises a recycle line for recycling the H₂S-enriched gas exiting the selective H₂S-absorption unit upstream of or directly into the Claus furnace.

The absorbing units usually comprise a regeneration system for the absorbing solution that comprises a stripping column with a reboiler and reflux drum. The absorbing solution is recovered at the bottom of the stripping column and is recycled into the absorbing unit. A gas stream enriched with acidic compounds is recovered at the head of the column and may be recycled upstream of or directly in the Claus unit. Therefore, the device may further comprise a recycling line for injecting the gas stream enriched with acidic compounds which is recovered at the head of the column upstream of or directly into the Claus unit.

The invention is further described in the FIGS. 1 and 2. These examples are offered to illustrate the invention and should in no way be viewed as limiting the invention.

FIG. 1 provides a schematic view of a classical CO₂ recovery unit, as known in the prior art. In FIG. 1, a sour gas is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas and an acid gas containing 50% of carbon dioxide and 50% of hydrogen sulfide. The acid gas then enters a Claus unit at a pressure of 2 bar wherein the hydrogen sulfide is converted into elemental sulfur. Then, the exiting mixture enters the hydrogenation reactor and then the quench contactor of the Tail Gas Treatment Unit (TGTU) to reduce the sulfur compounds leading to a hydrogenated tail gas mixture composed of 80% of nitrogen, 5% of hydrogen, 1% of carbon monoxide and 10% of carbon dioxide. At the outlet of quench contactor, said mixture enters the selective H₂S-absorption unit wherein it is contacted with an H₂S-selective amine based solvent in order to selectively capture H₂S.

Typically, MethylDiEthanolAmine (MDEA) is used as a common H₂S-selective amine solvent to capture the CO₂ from flue gas. After the step of absorption, the chemical amine solvent enriched in hydrogen sulfide is sent to a regenerator operating at a pressure comprised between 2 bara to recover the amine solvent depleted in acidic compounds (mainly H₂S) and to provide a stream which comprises 33% of H₂S and 66% of co-absorbed CO₂. Said stream is then recycled to the Claus furnace.

The off gas exiting the selective H₂S-absorption step is then introduced into an acid gas absorption unit wherein it is contacted with a non-selective amine-based solvent. Typically, MonoEthanolAmine (MEA) is used as a common non-selective amine-based solvent to capture the acid gases from the off gas. After the step of absorption, the chemical amine solvent enriched in carbon dioxide is sent to a regenerator operating at a pressure comprised between 2 bara to recover the amine solvent depleted in acid gases and to provide a stream which comprises 500 ppm of H₂S and 99.95% of CO₂ (dry basis).

The off gas exiting the acid gas absorption unit is then sent to the incinerator.

FIG. 2 provides a schematic view of a high-quality native CO₂ recovery unit for performing the method of the present invention.

In FIG. 2, a sour gas is introduced into an acid gas removal unit (AGRU), thereby providing a sweet gas and an acid gas containing 50% of carbon dioxide and 50% of hydrogen sulfide. A classical sweetening method using a chemical, a hybrid or a physical solvent is used as an Acid Gas Removal Unit (AGRU). The acid gas then enters a Claus unit at a pressure of 2 bar wherein the hydrogen sulfide is converted into elemental sulfur. Two streams exit from the Claus unit: a stream of elemental sulfur and a tail gas mainly comprising N₂, CO₂ and sulfur compounds. Then, the tail gas enters the hydrogenation reactor and then the quench contactor of a Tail Gas Treatment Unit (TGTU) in order to reduce the sulfur compounds present in the tail gas, leading to a hydrogenated tail gas mixture composed of 80% of nitrogen, 5% of hydrogen, 1% of carbon monoxide and 10% of carbon dioxide. At the outlet of quench contactor, said mixture enters the acid gas absorption unit wherein it is contacted with a non-selective amine-based solvent. Typically, MonoEthanolAmine (MEA) is used as a common non-selective amine-based solvent to capture the acid gases from the hydrogenated tail gas. The off gas exiting the acid gas absorption unit is then sent to the incinerator.

The regenerated acid gas from the absorption unit which comprises 5% of H₂S and 95% of CO₂ then enters the selective H₂S-absorption unit wherein it is contacted with an H₂S-selective amine based solvent in order to selectively capture H₂S.

Typically, MethylDiEthanolAmine (MDEA) is used as a common H₂S-selective amine solvent to capture the H2S from the previously mentioned acid gas mixture. After the step of absorption, the chemical amine solvent enriched in hydrogen sulfide is sent to a regenerator operating at a pressure comprised between 2 bara to recover the amine solvent depleted in acid gases and to provide a stream which comprises 20% of H₂S and 80% of co-absorbed CO₂. Said stream is then recycled to the Claus unit.

The treated gas exiting the selective H₂S-absorption unit comprises 100 ppm of H₂S and 99.99% of CO₂ (dry basis).

The embodiments above are intended to be illustrative and not limiting. Additional embodiments may be within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention. 

The invention claimed is:
 1. A device for treating a hydrocarbon feed gas stream containing at least carbon dioxide and hydrogen sulfide to recover a purified CO₂ gas stream, the device comprising in the direction of flow: an acid gas removal unit; a Claus unit; a tail gas treatment unit for removing sulfur components wherein the tail gas treatment unit comprises a hydrogenation reactor for converting sulfur compounds of the tail gas stream into H₂S, a quench contactor for removing water from the gas stream and a non-selective acid gas absorption unit which comprises an amine based solvent for separating carbon dioxide and hydrogen sulfide from the other constituents of the tail gas stream, said amine-based solvent adsorbing both carbon dioxide and hydrogen sulfide; a selective H₂S-absorption unit; and an incinerator connected at an outlet of the non-selective acid gas absorption unit for incinerating the off gas exiting the non-selective acid gas absorption unit.
 2. The device according to claim 1, wherein the tail gas treatment unit further comprises a feed inline burner or a tail gas heater before the hydrogenation reactor.
 3. The device according to claim 1, wherein the selective H₂S-absorption unit comprises a recycle line for recycling the H2S-enriched gas stream upstream of or directly to the Claus furnace. 